The present invention relates to an ultrafiltration system for removing impurities from liquids, such as water, and more particularly to a modular ultrafiltration system having an automatic filter regeneration capability.
Industrial processes require high purity water in large quantities for many different purposes, such as in paper pulp processes, cleaning components, producing steam, and formulating chemical solutions such as photoresists, etchants, plating baths, drugs, cosmetics, and a great many other products. Impurities found in municipal tap water can create large problems for manufacturers. Even microscopic contaminates can be disastrous, for example, in the manufacture of integrated circuits where any such contaminates can ruin the electronic circuitry embedded in the microchip. In the manufacture of foods and beverages, contamination can produce odors, discoloration, undesirable tastes and ultimately lead to outright spoilage. For these and other reasons it is necessary to purify water prior to its use in manufacturing operations. Additionally, with more stringent anti-pollution standards and the increasing cost of water, it has become necessary to treat most waste water or effluent streams leaving manufacturing facilities in order to control the biological oxygen demand (BOD), color, temperature, and pH thereof prior to discharge from a processing plant into a water course, lake, stream, pond or the like.
One technique that has proven quite useful and versatile in the removal of a large variety of pollutants and foulants from water influents and effluents is, for example, the ultrafiltration process disclosed in U.S. Pat. No. 3,758,405. However, the use of ultrafiltration membranes as disclosed in said patent necessitates frequent and rather difficult cleaning operations because of fouling and membrane failure caused by scale, slime or other foulant layer build up on the surface of the ultrafiltration membrane. Typically, such membranes require almost daily cleaning with extreme care as to the cleaning agents, temperature and pH conditions employed in order to prevent chemical attack or degradation of the membrane itself.
Ultrafiltration is a membrane process for the concentration of dissolved materials in aqueous solutions. A semipermeable membrane is used as the separating agent and pressure is used as the driving force. In an ultrafiltration process, a feed solution is introduced into a membrane unit or cell where water and certain solutes pass through the membrane. The membrane has a predetermined pore size and the feed solution is applied under a hydrostatic pressure. Solutes, whose sizes are greater than the pore size of the membrane, are retained and concentrated. The pore structure of the membrane thus acts as a molecular filter, passing some of the smaller size solutes and retaining the larger size solutes. The pore structure of this molecular filter is such that it does not become plugged because the solutes are rejected at the surface and do not penetrate the membrane. Furthermore, there is no continuous build-up of a filter cake which has to be removed periodically to restore flux (rate of solution transport through the membrane) since concentrated solutes are removed in solution. However, slimes, scales and other foulants such as humic acid (a forest floor decomposition product often times found in raw water) can build up on the membrane surface increasing the system pressure and reducing the flux thereby necessitating frequent cleaning or "regeneration" thereof.
In commercial operation, the number of ultrafiltration cells or "filter modules" to be used is determined by the total volume of the stream to be treated, the membrane area, and the separation efficiency which is affected by composition and pH of the stream, temperature and pressure of operation, and feed flow rate through the membrane number of ultrafiltration cells required can be easily calculated in a conventional manner. In addition, in order to avoid process disruption from membrane fouling and high operating pressures, cells have, in the past, been arranged in stages separated by pumps so that the stream can be passed sequentially through each stage. In this manner, a stage or stages can be removed from the system to enable membrane cleaning without closing down the entire ultrafiltration system.
In ultrafiltration systems known to date, the removal of filter modules for cleaning has been done manually, which is time consuming and not cost effective. It would therefore be advantageous to provide an ultrafiltration system with automatic or semi-automatic controls for effecting the regeneration of filter modules.
In order to provide such operation, it would be further advantageous to provide a means for detecting when a filter module is in need of regeneration. Such detection would enable the triggering of automatic controls to start the regeneration process. For economic reasons, it would be advantageous to provide a single regeneration apparatus which could be used to clean a plurality of filter modules in need of regneration, one at a time. When the regeneration apparatus is in use for cleaning one filter module, it would be advantageous to leave any additional filter modules in need of regeneration in the ultrafiltration system, taking such additional modules out of the system one at a time only during the period in which they are being regenerated.
The present invention relates to such an ultrafiltration system.